1. Field of the Invention
The invention relates to culture plates or dishes with a guard for preventing inadvertent splashing of fluid from the culture plate or dish.
2. Description of the Related Art
Culture plates or dishes are used for culturing cells, bacteria or other biological materials. The typical culture dish is formed from a transparent plastic and has a substantially flat bottom wall, a short side wall enclosure that extends up from the bottom wall and an open top. The bottom wall typically is circular and the side wall typically is cylindrical. However, rectangular culture dishes are known.
A liquid growth media is placed in the culture dish and a small sample of the cells, bacteria or other biological materials are placed in the liquid growth material. A transparent cover then may be placed over the open top of the side wall to provide a substantially controlled environment in which growth will occur. Samples of the materials growing in the culture dish may be taken periodically to assess characteristics of the sample over time. Additionally, controlled amounts of liquid media may have to be added to or removed from the culture dish periodically.
The culture dish may have to be moved from one place in a laboratory to another. Such movement necessarily requires acceleration, deceleration and directional changes of the culture dish. These movements create a wave phenomena in the liquid media stored in the culture dish. As noted above, the side walls of a culture dish are very short, and hence even a small wave in the liquid media can cause the liquid media to splash out of the culture dish. Many culture dishes have a bottom wall with a fairly large surface area (e.g., 500 cm2). The wave effects generated in such a large culture dish easily can exceed the height of the side wall, and hence significant amounts of liquid media can splash from the culture dish. Splashing reduces the volume of liquid media and biological materials in the culture dish, and hence can affect the laboratory analysis. Additionally, splashing of liquid media and other biological materials can cause contamination in the laboratory. For example, liquid media in one culture dish can inadvertently splash into an adjacent culture dish.
The problem of splashing from the culture dish has been known, and solutions to that problem have been considered. For example, U.S. Pat. No. 5,593,891 shows a culture dish with a circular bottom wall, a cylindrical side wall and a splash guard extending inwardly from the side wall. In some embodiments, the splash guard is formed unitarily with the side wall. However, these unitary structures are difficult to mold. In other embodiments, however, the splash guard is snapped into engagement with the mounting structure formed circumferentially on the side wall at or near the open top. In still other embodiments, the splash guard telescopes over or into the open top of the side wall. Splash guards that telescope over the side wall are undesirable because they add to the overall dimensions required for the culture dish.
Rectangular or square culture dishes have advantages over round culture dishes with cylindrical side walls. For example, round culture dishes can be arranged on a support surface with the cylindrical side wall of each culture dish being tangent to the cylindrical side walls on as many as four other identical culture dishes. This spacial arrangement of culture dishes result in substantial dead space between the points of tangency. Hence, circular culture dishes result in an inefficient use of space. Additionally, biological specimens are likely to grow differently at different locations in a culture dish based on environmental factors, such as the location and angle of light and minor temperature variations due to local environmental conditions. It is difficult to ensure uniform orientation of round culture dishes after the culture dishes have been moved for sampling or replenishment of the liquid growth media. Additionally, it is difficult to measure variations in the growth characteristics of cultures at various locations across the bottom wall of the culture dish. Still further, it is difficult to pour liquid media from a round culture dish in view of the relatively large radius of curvature on the cylindrical side wall.
Square and rectangular culture dishes overcome the above-identified problems. In particular, square culture dishes can be arranged close together, thereby achieving an efficient use of space in a laboratory. Square culture dishes also are easily oriented on the supporting surface, and rectangular quadrants can be assigned easily to a square culture dish to determine and track differences in culture growth characteristics at different coordinates across the bottom wall. However, square culture dishes are not conducive to receiving a separately mountable splash guard. More particularly, a splash guard on a circular culture dish will exert forces uniformly against the cylindrical side wall of the dish. In theory, the side walls of a square culture dish could be formed with a bead or groove for engaging a mating structure on a square splash guard. However, it is difficult to achieve uniform forces along such a rectilinear array of interengaged surfaces, and stress concentrations are likely to exist. The existence of non-uniform engagement forces around the peripheries of a square splash guard can complicate the mounting of the splash guard and can damage either the splash guard or the side walls. Additionally, gaps may exist between mating surfaces of the square splash guard and the side wall. The liquid media can splash through or can accumulate in such gaps. Liquid media that accumulates in gaps between the square splash guard and the side walls may cause a culture growth that is much different than the culture growth on the bottom wall of the dish. Thus, although square culture dishes offer advantages over cylindrical culture dishes, the square culture dishes are not well suited to the splash guards that have been employed with round culture dishes.